An organic electroluminescence (hereinafter, referred to as “organic EL”) display device includes a light-emitting element provided in each of a plurality of pixels and displays an image by controlling light emission of each of the light-emitting elements individually. The light-emitting element has a structure in which a layer containing an organic EL material (hereinafter, also referred to as an “organic layer”) is interposed between a pair of electrodes, one of which is an anode and the other of which is a cathode. In such an organic EL display device, one of the electrodes is provided in each pixel as a pixel electrode, and the other electrode is provided over the plurality of pixels as a common electrode applied with a common voltage. In the organic EL display device, a voltage is applied to the pixel electrode in each of the pixels individually to control the amount of electric current flowing in the light-emitting layer and thus to control the light emission of each of the pixels.
Usually in a manufacturing process of such an organic EL display device, a metal mask is used to form an organic layer. The organic layer is formed by patterning performed by use of a metal mask. For example, Japanese Laid-Open Patent Publication No. 2004-165068 discloses a method for forming an organic layer by a vacuum vapor deposition method by use of a metal mask having an opening for each of pixels.
Use of a metal mask requires dedicated equipment and periodical maintenance.
In addition, use of a metal mask includes the following problem. During a patterning step, a substrate and the metal mask may contact each other, which may generate particles. Such particles, together with moisture entering the inside of the display device, decrease the performance of the light-emitting element. This shortens the life of the display device.
In such a case, a manufacturing process using no metal mask to pattern the organic layer (so-called maskless process) is desired. Such a process is expected to decrease the manufacturing cost.
According to one maskless process that has been explored, an organic film acting as a light-emitting layer is patterned by laser ablation. This method removes unnecessary parts of the organic film by laser in a patterning step. However, since a cathode film and a sealing film are formed after the patterning step, parts of the organic film scattered by the laser ablation become particles in a later step and may cause dark spots.
An organic EL display device including an organic EL layer as a light-emitting layer has the following problem. The organic EL layer is very weak against moisture. If moisture enters the display device from outside and reaches the organic EL layer, dark spots may be generated. Such an organic EL display device uses an organic material such as an acrylic resin, a polyimide resin for an organic planarization film or a bank. Such an organic material acts as a path that transfers moisture. Thus, moisture entering from outside may reach the organic EL layer and deteriorate the display device.